Image: NASA/JPL-Caltech/T. Pyle
By Duncan Geere, Wired UK
Astronomers have published a study revealing that NASA’s exoplanet-hunting Kepler telescope has spotted two planets orbiting two suns for the first time.
The find proves that circumbinary planetary systems can not only form in, but continue to withstand, the intense pressures exerted by a binary star system — until now, astronomers had only been able to identify binary star systems with one planet in orbit, a find that was confirmed in 2011 when Kepler-16b was spotted.
“The presence of a full-fledged circumbinary planetary system orbiting Kepler-47 is an amazing discovery,” commented Greg Laughlin, professor of astrophysics and planetary science at the University of California, in a press release. “These planets are very difficult to form using the currently accepted paradigm, and I believe that theorists, myself included, will be going back to the drawing board to try to improve our understanding of how planets are assembled in dusty circumbinary disks.”
Circumbinary planets only came to light in the last two decades, with several discoveries being flagged up ahead of Kepler’s 2011 confirmation. Until then, Luke Skywalker’s home planet Tatooine in the Star Wars films was the most famous example of a circumbinary planet. Just one planet orbiting a binary system is an impressive feat, considering the dynamics of the gravitational pull being exercised by two stars orbiting one another. Astronomers have theorised that more often than not, the complex gravitational system would result in young planets being forced out or cause planetary collisions.
According to the study, published in the journal Science, the two planets — Kepler-47b and Kepler-47c — have most likely thrived because of their relatively small size, their mass being affected by the binary system they grew up in.
“In contrast to a single planet orbiting a single star, the planet in a circumbinary system must transit a ‘moving target.’ As a consequence, time intervals between the transits and their durations can vary substantially, sometimes short, other times long,” explained Jerome Orosz, a professor of astronomy and lead author of the paper, in the press release. “The intervals were the telltale sign these planets are in circumbinary orbits.”
Nearly 5,000 light-years from Earth, located in the Cygnus constellation, inner planet Kepler-47b orbits its stars in just under 50 days and is presumed to be a hostile environment with a searing hot surface. It has a radius three times that of Earth’s, which makes it the smallest ever circumbinary planet identified. Outer planet Kepler-47c has a radius 4.6 times that of Earth’s and orbits the binary stars every 303 days.
Like Earth, that distance puts it in the habitable zone where liquid water could potentially exist, though its likely Kepler-47c is an inhospitable gaseous planet surrounded by thick clouds. “While the outer planet is probably a gas giant planet and thus not suitable for life, large moons, if present, would be interesting worlds to investigate as they could potentially harbour life,” commented Orosz’ colleague and co-author William Welsh in another press release.
The binary stars, which orbit one another every 7.45 days, also differ vastly in size, with one around the same size as our Sun but 84 percent as bright and the other a third of the size of our Sun and one percent as bright.
Despite the planets both being considered inhospitable, the existence of a full circumbinary planetary system proves that there are even more possibilities for the existence of life in the universe, and that Kepler truly has its work cut out for it — Nasa’s phones are presumably ringing off the hook with Star Wars fans hoping the next find will be of a hospitable circumbinary planet with a scenic view of its two suns.
Thanks to: http://www.ascensionwithearth.com